Flame detecting means



FLAME DETECTIN G MEAN S William A. Ray, North Hollywood, Calif., assignor to General Controls Co., Glendale, Calf., a corporation of California Application October 26, 1953, Serial No. 388,099

2 claims. (CI. 158-28) as the radiaton from the flame itself, with the result that a false indication may be produced, leading to the creation of a dangerous situation.

Briefly, the present invention relates to improved means and techniques for producing an ndication or 'control which takes into account the radiaton from the heated furnace walls as well as the radiaton from the flame, by establishing a certain "diiferential effect, such differential effect being in accordance With the difference in radiation due, on the one hand, to the flame itself and, on the other hand, to the furnace walls or any other body heated by the flame.

For these general purposes, two radiaton receiving means are provided, one to receive radiaton from the flame and furnace wall, and the other means being arranged to receive radiaton from the fnrnace wall alone, which is heated by the flame. The radiations as thus received are efiectively measured and are each represented by corresponding electrical quantities, such quantites being effectvely subtracted so` as to produce a third electrical quantity, i. e., a net voltage which has a relatively large value when a flame is present and which has a relatively small value or zero value when there is no flame, such net voltage being amplified to produce either an indication or to control the fiowof fuel to the flame producing means.

One aspect of the present invention nvolves the use of radiaton .receiving elements such as, for example, wires or thcrmocouples disposed in different arms of a bridge circuit to achieve the above-indicated diiferential ettect.

Another aspect of the present invention involves the transmission of the energy from the flame and heated brick Wall onto elements in diiferent arms' of a bridge circuit through a spectrum producing element whereby such elements are heated selectively in accordance with energy having a frequency characterstic of the flame and the heated furnace Wall or brick work.

It is, therefore, a 'general object of the present invention to provide means and techniqnes of the character indicated above.

A specific object of the present invention is to provide improved means and 'techniques of this character which require no moving elements. I

Another specific object of the present provide means and technques of this character which are relatively insensitive to sporadic fluctuations in intensity of the flame.

Another specific object of the present invention is to provide an arrangement of this character which is capable of withstanding high ambient temperaturesand' invention is to nited States patent Oj in accordance with a particular band of wave lengths in the flame spectra.

Another specific object of the present invention is to provide an arrangement of this character which avoids the use of filter elements and the disadvantages attendant upon the use of a filter.

apparatus shown partly in structural form and partly in schematic form. y

Figure 2 illustrates the condition wherein the radiaton sensitive elements are resistance wires. Figura 3 illustrates the condition wherein the radiaton sensitive elements are thermocouples.

The furnace 10 is of conventional structure and is considered to be lined with a refractory material such as fire brick, and is defined by the fire walls 12, 13, 14 and 15. The conventional flame producing means 16 serves to produce flame :17, such flame producing means being sup plied with fuel which normally fiows from the fuel inlet zothrough the solenoid valve 21 through the fuel outlet valve 22, such outlet being deemed to be in communication With the conventional apparatus 16.

i The flame 17 may be considered as that being due either to' the burning of 'oil or to the burning of gas or other i fuel. r e

` Two radiaton channels are provided, namely, radiaton channels 25 and 26, in the form of tubes. The tube 25 is oriented so as to receive the radiaton not only from* the flame 17, but'also from the heated furnace wall 13 along a path indicated by the line 28, such radiaton being focused by a condensing lens 29 and applied through a,

suitable' light dispersing means 30 such as a prism or dfirac'tion grating onto the element 32. The other radiation tube 26 is oriented so as to receive the radiaton from one of the heated furnace walls only and such radiaton passes through the lens 37 and impinges on the light dispersing'element 38 in the nature of a prism or difi'ractio-n grating so that a'selected band of wave lengths characteristicof the radiaton from the heated furnace Wall is directed onto the other radiaton receiving element 34. The optical system associated with the element'32 is such thatthe element 32 has selectively directed thereto radiaton of `a band of frequenies characteristic of the flame,

itseli a r The radiaton receiving elements 32 and 34 may either be 'a wire having appreciable electrical resistance or a thermoeouple, such wire or thermocouple being either exposed to the atmosphere or enclosed inuan evacuated chamber such as an evacuated glass or quartz envelope which, of course, allows the passage of the desired band of frequencies. I r

The elements 32'and 34 are disposed in different arms of the bridge'cir'cuit 40 .to produce a difierential efiect.

In the instance when' the elements 32 and 34 are resstance 3 elements, the' resistance of such elements changes in accordance with` the` radiation` impinging thereom and in that nstance when the elements 32 and 34 are thermocouples, voltages are developed by such thermocouples in -resporse to the` amountof radiation impinging thercon. In either case, it is understoodthatthe term `"elec'trical characterstc'" as` used in connection with elements` 32 and -34 'has reference either to a change in-property of theelernents such as a change in resistance, or a change in an output voltage. i V i "Theelement 32 is in` a first arm of the` bridge 40, the element 34 is in a second arm of the bridge, the resistance 42 is in a third armof the bridge and the resistance'43 is in-a fourth arm` of the bridge. The bridge is essentially &direct-current type of bridge and is supplied with' con- `tinuous current fromthe contnuous voltage source 45.

The so-called galvanometer arm" of the bridge comprises a DHC. amplifier 46 which serves to control the flow of fuel tothe flame producing means 16.

It is understood that in the presence of a flame,` sufficient direct current voltage `is applied to the amplifier` 46 to cause solenoid `valve 21 to be energized' tothereby allow the` flow of fuel to the burner 16; and, when the flamelT is extnguished for any reason whatsoever, the solenoid `valve 21 is deenergized to allow the spring means normally associated with conventionalsolenoid valves of this character to interrupt the 'flow of fuel to the burner or` flame producing means 16. v "The alternating current source 50 connected in the so-called battery arm of the bridge s for purposes ,of

supplying a heating current to the serially connected radiation receiving elements 32 and 34 to thereby artificially heat the same to an elevated temperature so as to regulate its rate of response to radiant conditions. Pref erably, radiation reecting elements 60 and 61 are disposed` adjacent to the elements` 32 and 34" for directing the radiation from the furnace onto the 'elements 32'and 34res`pectively and *also for the purpose of directing that gized electrically to produce an electrical `quantity which V represents the i radiation from the furnace wall itself. These two electrical quantities are etfcctivelycompared to produce a third electricalquantity which appears'at the input terminals to the amplifier 46. i

' Thelght dispersing element 30 serves to eflectively separa'tethe incident radiation into aspectrum as is-well knownwith this type of element and only a portion of such spectrum corresponding to a particular band of fre quencies is allowed to have its effect on the element 32. Thisparticular band of frequencies is one which is'char acteristc of .the flame produced by the flame 17. In order to separate the dispersed energy-so that this result may be achieved, suitable means such as a slitted shield 70-s disposed between theelements 30 and 32 with energy' of a parteular band of`frequencies only which is characteristic' of the flame itself being allowed to impinge=on the element 32. This particular band of frequencies may correspond either to a particular emission band in the fiame spectre. or to a band of frequencies` beyond the range o freque'ncies wheren copious amount of radiation results from'the heated furnace wall. 'The radiaton from the hez ted furnace wall -i not appreciahly unlike that from a so-called "black body which follows well known formulae and which has a well known` energy versus frequency pattern with the maximum energy occurring at a particular frequency and with most of the energy lying within a relatively narrow frequency range. Thus, the element 34 may be subjected only to energy in this particular narrow frequency range which passes through a slt in the slitted plate 72 disposed between the elements 38 and 34; while theelement 32 may be subjected to energy from the flame having either a frequency band outside of such narrow' frequency range or `subjected to a frequency band within such narrow frequency range and in either case, such frequency band preferably corresponds to' an emission' band in the flame spectra.

It is noted that the arrangement is one in which differences in intensity of radiation are compared to produce a differential effect, and that the apparatus is preferably rendered frequency sensitive, using radiation dspersing and separating means, exemplified by the elements i tion have been shown and described, it will be obvious tothoseskilled in the art that changes and modifications may he made without depar'tng from this invention in its broadcr aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scopo of this invention.

I claim:`

l. In `apparatus for controlling the presence of a flame produced by a flame producing means, a body, flame producing means for producing a flame which is present in'an enclosure having said body heated by said flame produced` by flame producing means, first frequency selectve means for separating energy radiated from said flame and having a frequency band characteristic of said flame, second frequency selectve means for separating energy radiated from said body and having a frequency .bandcharacteristic of said heated body, and means for comparing the first mentioned energy with the second mentioned energy to control said .flame producing means.

. 2. In apparatus for controlling the presence of a flame in the vicinity ora body heated by a flame produce'dby flame producing means, a body, a flame producing means for. producing a flame to heat said body, a pair` of radiation receiving elements, one of said elements receiving 'adiation from' the flame and the body, the other one 56 of, said pair of elements receiving radiation from the body only, means for comparing the energy received on the one hand, by said one element with the energy received,non the other hand, by said other element. to

obtain a comparison between the two energies, means for controllng said flame producing means to deactivate the same when said comparson 'indicates substantial equality between said energies, and frequency selectve means for subjecting said one element to energy having a frequency band which is characteristic of the flame, and frequency selectve means for subjecting said other element to` energyhaving a frequency band characteiistic of said body.

References Cited inthe file of this patent UNITED STATES PATENTS 

